PROJECT SUMMARY/ABSTRACT With the introduction of the `Heat-not-Burn' (HnB) tobacco products the landscape of tobacco market has changed yet again. Emerging HnB products purport to reduce exposure to toxicants compared with combustible nicotine products such as tobacco cigarettes by avoiding directly burning tobacco and instead heating tobacco. Philip Morris International submitted an application to the US FDA for their HnB product iQOS to be authorized as a modified risk tobacco product (MRTP). Claims of lowered risk of iQOS (non-combustible tobacco product) compared to conventional cigarettes (combustible tobacco product) are based almost exclusively on industry-funded research, and reliable independent research on their health effects is not available to support these claims. Independent research is therefore urgently needed to provide a balanced view on the potential health impact of HnB products. There is a critical knowledge gap in the potential impact of HnB aerosols on pulmonary inflammation and immunity to pathogens that cause respiratory diseases. Our proposal seeks to utilize the combined expertise of two principal investigators and our portfolio of standardized assays to demonstrate for the first time if chronic exposure to HnB aerosol has the potential to result in alteration of pulmonary inflammation, morphological changes in the lung and modify the immune response. The overall goal of this application is to determine if inhalation of HnB aerosol has the potential to result in pulmonary damage and suppress the immune response to vaccination. In a side?by-side comparison format, we will compare the effect of HnB aerosol to effects caused by tobacco cigarette smoke or electronic cigarette aerosol. Our premise will be tested in an established mouse model and will use both male and female mice to evaluate the potential effect of sex of the host. As cigarette smokers may be inclined to switch to HnB products under the assumption that they are less damaging than conventional cigarettes, therefore this premise will be tested by us in `switching' experiments. In Specific Aim 1 we will test the hypothesis that chronic inhalation exposure to HnB aerosol has the potential to cause lung inflammation and result in changes in inflammatory cell numbers and cytokines levels in the lung and this milieu alters the innate immune response. In Specific Aim 2 we propose to test the hypothesis that chronic inhalation of HnB aerosol creates a milieu in the lungs which has the potential to impair adaptive immune responses to a vaccine and we will examine the ability of the response elicited to clear an acute pulmonary infection. Finally, in Specific Aim 3, we will test the hypothesis that transition to HnB usage following tobacco smoke exposure could hinder resolution of inflammation that can be achieved by true cessation. The findings from this proposal would have direct regulatory implications and real world relevance as they will provide novel insights on absolute and relative (as compared to tobacco and electronic cigarettes) health risk of HnB products.